Does nerve regeneration restore normal functional patterns in mouse barrel cortex?
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Animals↗
Biomedical subjects
G Bronchti
Publications and source records attributed to G Bronchti.
Altered sensory processing in the somatosensory cortex of the mouse mutant barrelless.
Mice homozygous for the barrelless (brl) mutation, mapped here to chromosome 11, lack barrel-shaped arrays of cell clusters termed "barrels" in the primary somatosensory cortex. Deoxyglucose uptake demonstrated that the topology of the cortical whisker representation is nevertheless preserved. Anterograde tracers revealed a lack of spatial segregation of thalamic afferents into individual barrel territories, and single-cell recordings demonstrated a lack of temporal discrimination of center from surround information. Thus, structural segregation of thalamic inputs is not essential to generate topological order in the somatosensory cortex, but it is required for discrete spatiotemporal relay of sensory information to the cortex.
Animals↗
Vision influences paw-preference in mice.
We studied the influence of vision on the expression of handedness in mice. In one experiment we submitted adult mice that had an opaque scleral contact lens fitted to one eye, to a paw-preference testing procedure. When the eye was occluded before training, the animals showed a clear preference for the paw ipsilateral to the open eye; however, we could not induce a shift in a previously determined, natural, paw-preference when the lens was placed over the eye ipsilateral to the spontaneously preferred paw; these results indicate that vision plays a role in the animal's choice of a paw during the learning phase of the paw-preference test. In a second experiment adult mice that had been subjected to unilateral eye removal at birth, underwent the same test. The enucleation did not appear to influence handedness with respect to both direction and strength. The latter result--we propose--reflects a reorganization of the visual system induced by neonatal enucleation.
Animals↗
Barrelfield expansion after neonatal eye removal in mice.
We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in mice. Areas were measured in drawings made from tangentially cut Nisslstained sections of somatosensory cortex. We compared areas of 29 barrels, corresponding to 29 mystacial vibrissae, between adult mice enucleated at birth (n = 13) and their intact littermates (n = 13). Multivariate analysis of variance showed that the barrelfield was larger in enucleated mice. This expansion was mainly due to the increase in areal extent of the barrels corresponding to the dorsalmost row of vibrissae, and of a set of barrels corresponding to rostral vibrissae near the nose and mouth. Evidently, early enucleation has a significant cross-modal effect on the somatosensory cortex.
Aging↗
Retinal projections in the blind mole rat: a WGA-HRP tracing study of a natural degeneration.
The mole rat Spalax ehrenbergi is a fossorial rodent. Although its peripheral visual system--eye and optic nerve--is highly degenerated, it shows some sensitivity to light. However, in the usual sense, it is essentially blind. An auditory take-over of the visual lateral geniculate nucleus and at least part of the visual cortices was recently demonstrated. In order to visualize the retinal projections during ontogeny, we used an anterograde tracing technique, with monocular injection of wheat germ agglutinin-labeled horseradish peroxidase (WGA-HRP). In the newborn mole rat the retina projects to most of its normal targets as compared with seeing rodents, with bilateral projections to the suprachiasmatic nuclei, the dorsal and ventral lateral geniculate nuclei, the lateroposterior nuclei, the optic tract nuclei and the superior colliculi. During the course of ontogeny, the retinohypothalamic connection is stabilized but the main optic tract undergoes progressive degeneration. In adults, only a few retinal fibers enter the contralateral ventral lateral geniculate nucleus, the lateroposterior nucleus, the optic tract nucleus and the superior colliculus. No retinal fibers could be detected in the dorsal lateral geniculate nucleus. Thus, the retinofugal projections in the adult mole rat could explain its reduced sensitivity to light, whereas the complete degeneration of the retino-dorsal lateral geniculate nucleus projection could underlie the invasion of auditory input into this normally visual center.
Animals↗
Invasion of visual cortex by the auditory system in the naturally blind mole rat.
Previously we have shown that the dorsal lateral geniculate body (LGB), which is strictly visual in sighted mammals, receives a strong auditory input in the naturally blind mole rat (Spalax ehrenbergi). Here we show with the 2-deoxyglucose technique and with single-unit recordings that in this species the initially non-degenerated visual cortex, as defined by its connection with LGB, is also activated by the auditory modality. These findings suggest that cross-modal compensation may occur as a natural consequence of the degeneration of a sense organ.
Animals↗
Auditory pathway and auditory activation of primary visual targets in the blind mole rat (Spalax ehrenbergi): I. 2-deoxyglucose study of subcortical centers.
The blind mole rat Spalax ehrenbergi is a subterranean rodent that shows striking behavioral, structural, and physiological adaptations to fossorial life including highly degenerated eyes and optic nerves and a behavioral audiogram that indicates high specialization for low-frequency hearing. A 2-deoxyglucose functional mapping of acoustically activated structures, in conjunction with Nissl/Klüver-Barrera-stained material, revealed a typical mammalian auditory pathway with some indications for specialized low-frequency hearing such as a poorly differentiated lateral nucleus and a well-developed medial nucleus in the superior olive complex. The most striking finding was a marked 2-deoxyglucose labeling of the dorsal lateral geniculate body and of cortical regions that correspond to visual areas in sighted rodents. The results render the blind mole rat a good model system for studying natural neural plasticity and intermodal compensation. In this report, we confine ourselves to the subcortical levels. The cortical level will be dealt comprehensively in a following paper.
Acoustic Stimulation↗
"Warm-up" along dimensions of movement in the ontogeny of exploration in rats and other infant mammals.
When some infant mammals are placed outside their nest, a sequence of exploratory behavior occurs, displaying a regular buildup and spread of activity. This "warm-up" involves repetition of movement along specific dimensions and an orderly transition from one dimension to the next, with cephalocaudal recruitment of body and limb segments. A similar principle of organization applies to neurological recovery from lateral hypothalamic akinesia.
Animals↗